1
2/* pngrio.c - functions for data input
3 *
4 * Last changed in libpng 1.6.24 [August 4, 2016]
5 * Copyright (c) 1998-2002,2004,2006-2016 Glenn Randers-Pehrson
6 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
7 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
8 *
9 * This code is released under the libpng license.
10 * For conditions of distribution and use, see the disclaimer
11 * and license in png.h
12 *
13 * This file provides a location for all input.  Users who need
14 * special handling are expected to write a function that has the same
15 * arguments as this and performs a similar function, but that possibly
16 * has a different input method.  Note that you shouldn't change this
17 * function, but rather write a replacement function and then make
18 * libpng use it at run time with png_set_read_fn(...).
19 */
20
21#include "pngpriv.h"
22
23#ifdef PNG_READ_SUPPORTED
24
25/* Read the data from whatever input you are using.  The default routine
26 * reads from a file pointer.  Note that this routine sometimes gets called
27 * with very small lengths, so you should implement some kind of simple
28 * buffering if you are using unbuffered reads.  This should never be asked
29 * to read more than 64K on a 16-bit machine.
30 */
31void /* PRIVATE */
32png_read_data(png_structrp png_ptr, png_bytep data, png_size_t length)
33{
34   png_debug1(4, "reading %d bytes", (int)length);
35
36   if (png_ptr->read_data_fn != NULL)
37      (*(png_ptr->read_data_fn))(png_ptr, data, length);
38
39   else
40      png_error(png_ptr, "Call to NULL read function");
41}
42
43#ifdef PNG_STDIO_SUPPORTED
44/* This is the function that does the actual reading of data.  If you are
45 * not reading from a standard C stream, you should create a replacement
46 * read_data function and use it at run time with png_set_read_fn(), rather
47 * than changing the library.
48 */
49void PNGCBAPI
50png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
51{
52   png_size_t check;
53
54   if (png_ptr == NULL)
55      return;
56
57   /* fread() returns 0 on error, so it is OK to store this in a png_size_t
58    * instead of an int, which is what fread() actually returns.
59    */
60   check = fread(data, 1, length, png_voidcast(png_FILE_p, png_ptr->io_ptr));
61
62   if (check != length)
63      png_error(png_ptr, "Read Error");
64}
65#endif
66
67/* This function allows the application to supply a new input function
68 * for libpng if standard C streams aren't being used.
69 *
70 * This function takes as its arguments:
71 *
72 * png_ptr      - pointer to a png input data structure
73 *
74 * io_ptr       - pointer to user supplied structure containing info about
75 *                the input functions.  May be NULL.
76 *
77 * read_data_fn - pointer to a new input function that takes as its
78 *                arguments a pointer to a png_struct, a pointer to
79 *                a location where input data can be stored, and a 32-bit
80 *                unsigned int that is the number of bytes to be read.
81 *                To exit and output any fatal error messages the new write
82 *                function should call png_error(png_ptr, "Error msg").
83 *                May be NULL, in which case libpng's default function will
84 *                be used.
85 */
86void PNGAPI
87png_set_read_fn(png_structrp png_ptr, png_voidp io_ptr,
88    png_rw_ptr read_data_fn)
89{
90   if (png_ptr == NULL)
91      return;
92
93   png_ptr->io_ptr = io_ptr;
94
95#ifdef PNG_STDIO_SUPPORTED
96   if (read_data_fn != NULL)
97      png_ptr->read_data_fn = read_data_fn;
98
99   else
100      png_ptr->read_data_fn = png_default_read_data;
101#else
102   png_ptr->read_data_fn = read_data_fn;
103#endif
104
105#ifdef PNG_WRITE_SUPPORTED
106   /* It is an error to write to a read device */
107   if (png_ptr->write_data_fn != NULL)
108   {
109      png_ptr->write_data_fn = NULL;
110      png_warning(png_ptr,
111          "Can't set both read_data_fn and write_data_fn in the"
112          " same structure");
113   }
114#endif
115
116#ifdef PNG_WRITE_FLUSH_SUPPORTED
117   png_ptr->output_flush_fn = NULL;
118#endif
119}
120#endif /* READ */
121